Switch calibration means



April 1968 s. A. MORGAN 3,379,844

SWITCH CALIBRATION MEANS Filed March 11, 1968 3 J5 4Q? 7Q 2 Sheets-Sheet 1 INVENTOR.

Aprifi 1968 s. A. MORGAN 3,379,844

SWITCH CALIBRATION MEANS Filed March ll. 1966 2 Sheets-Sheet 2 INVENTOR.

United States Patent 0 3,379,844 SWITCH CALIBRATION MEANS Samuel A. Morgan, Ann Arbor, Mich, assignor to King- Seeley Thermos C0., Ann Arbor, Mich, a corporation of Michigan Filed Mar. 11, 1966, Ser. No. 533,535 9 Claims. (Cl. 200139) This invention relates to a means for calibrating electric control switches, and more particularly to a novel combination of elements for adjusting the initial relationship of the contacts of a thermally actuated switch.

In a thermally actuated switch, a thermomotive member is provided which is adapted to move one contact either toward or away from its opposed contact when heated. In its more usual form, the thermomotive member is arranged to tend to separate the contacts when heated, the heat being derived either from a controlled heating element or from an auxiliary resistance heater connected in circuit with the contacts and arranged to be in heat transfer relationship with the thermomotive member. The form employing an auxiliary resistance heater is known as an infinite switch.

In order to select the temperature to be maintained by the heating element, adjustment means is provided which conveniently takes the form of a cam arranged to adjustably and resiliently displace one contact relative to the other contact, which displacement is commonly called contact overclosure. The angular position of the cam is indicated by a dial or the like including calibration legends which may indicate the corresponding rate of heat being delivered by the switch member. The accuracy of these legends, as indicators of the temperature level selected, depends on the initial calibration of the switch. Basically such initial calibration is accomplished by adjusting the initial position of one contact relatve to the other.

Accurate calibration is particularly ditlicult in the case of an infinite switch in which the heating element is intermittently energized wherein the temperature level is established by the ratio of closed to open contact time. This closed to opened contact time, or duty cycle, determines the percentage input of power. This calibration difficulty is particularly acute in the lower range of adjustments, however it is desirable to assure maximum accurary throughout the whole range. Calibration is ordinarily performed at some specified low setting, which is ordinarily chosen to be at a simmer producing heat level. In one prior art arrangement, a screw has been used for this purpose, either threaded through the mounting and arranged to engage the contact carrying arm, or threaded through a member interconnected with the contact carrying arm and extending through a hole in a portion of the mounting, with the head of the screw engaging the outer surface of the above mentioned portion.

For close and accurate adjustments, the use of a screw adjustment introduces a certain amount of undesirable error. There is a limit to the fineness of threaded pitch that is commercially and feasibly obtainable so that the adjustment is more coarse than is desirable. Even an extremely fine pitch thread has a certain amount of clearance at the pitch line, with the result that the longitudinal position of the screw may immediately change when the pressure on the screwdriver or other adjusting means is removed. A slight bend may result in a wobbling whereby a small turning of the screw may cause a relatively large change in calibration. There are problems of thread uniformity, possibly stripped threads, and/or eccentricity in the screw itself. In addition, the position of the screw may be altered as a result of vibration.

In certain other prior art forms, calibration is accomplished by pressing into position a specially constructed adjusting pin adapted to frictionally engage the walls of an aperture in the mounting. An automatic pressure device is utilized to exert pressure on the pin and is arranged to automatically release the pressure at the exact position representing the temperature level for which the dial is set. In contrast to a screw, such an adjusting pin is not effected by eccentricity or lack or straightness, since it is not rotated. Further it obviates all the defects of a threaded part, including lack of thread uniformity, stripping threads and pitch line clearance. It is not affected by vibration, since it is held tightly in its mounting by frictional engagement. However, in this form, certain parts of the switch are rendered more complex than with the present invention. A minimum in housing dimension is not maintained, and certain electrically live portions of the switch may be unnecessarily exposed.

Accordingly, it is one object of the present invention to provide an improved electrical switch.

It is another object of the present invention to provide an improved means for initially calibrating an electrical switch.

It is still another object of the present invention to provide a calibrating apparatus for a switch which is simple to use, reliable in operation and economical to construct.

It is a further object of the present invention to provide a calibrating apparatus for an electrical switch which improves the physical configuration of the switch.

It is still a further object of the present invention to provide a calibrating apparatus which reduces the exposure of electrically energized portions of the switch to the user.

For illustrative purposes the present invention is described as it is applied to an infinite switch, although its use is not intended to be limited thereto. Further objects, features, and advantages of this invention will become apparent from a consideration of the following description, the appended claims and the accompanying drawings in which:

FIGURE 1 is a perspective view of the exterior of a housing for a thermally actuated switch;

FIGURE 2 is a plan view of the contacts of the housing with the cover plate and cam mechanism removed;

FIGURE 3 is a sectional view taken along line 33 of FIGURE 2 showing the infinite switching construction;

FIGURE 3A is a sectional view taken along line 3A3A of FIGURE 3 illustrating the details of a preferred form of calibrating apparatus;

FIGURE 4 is a sectional view taken along line 44 of FIGURE 2;

FIGURE 5 is a fragmentary sectional view taken along line 5-5 of FIGURE 2, and illustrating the details of the cam operating mechanism; and

FIGURE 6 is another fragmentary sectional view taken along line 6-6 of FIGURE 4 and illustrating other details of the cam operating mechanism.

Referring to the drawing and particularly to FIGURE 1, the switch is preferably enclosed in a hollow housing 10 which is formed as a boxlike enclosure having an open side and various element suporting appendages integrally formed therewith. The housing 10 may be composed, for example, of a rigid phenolic resin which is molded into the desired shape. Closing the open end of the housing is a cover plate 11, held in place by suitable fastening means 12, taking the form of a pair of tabs engaging opposite sides of the housing. The cover plate 11 is formed with a calibrating aperture 13 which permits the user to calibrate the switch from the exterior of the housing, as will be more fully explained hereinafter. Extending through the cover plate and axial to the switch housing to a suitable bearing is a shaft 14, the outer end of which is secured to a knob and a dial 15a. The indicator legends on the dial 1511 provide an indication of the selected temperature level and may be compared with a reference mark 16 on the cover plate.

Within the housing 16 are a pair of switch structures, generally designated 17 and 18 (see FIGURE 2). Switch structure 17 provides two switches, each including one fixed and one movable contact. The movable contacts have a common support member 20, one end of which includes a contact portion 21 integrally formed with the support member and a second contact 22 suitably fastened to the support member 20. Support 20 is bifurcated at one end thereof, one portion 23 of which is fixed to housing 10 at an end of the support member 20 which is opposite to the contacts. In fastening the portion 23 to the housing, an aperture 24 is formed therein which receives a portion 23 of the support member 20, portion 23 forming a tab extending through the bottom of the housing. The extension of the tab forms a terminal member which may be connected to a line to be controlled by one of the contacts 21 or 22, or the terminal member provided by tab 23 may provide a common connection for both of the lines to be controlled by contacts 21 and 22.

The contact portion 21 is adapted to engage a fixed contact 26 which is formed as a blade projecting into the interior enclosure of the housing wherein the contact 26 is electrically connected, and may be integrally formed with, a second tab portion 28 projecting through the bottom of the housing 10 in a manner similar to the tab portion 23. Thus the tab 28 forms a second terminal which is controlled by the opening and closing of the matable contacts 21 and 26. The circuit from the tab 23 through the blade 20, contacts 21, 26 and tab 28 may form part of a pilot light circuit to indicate the closure of the contacts 21, 26 in a typical range circuit. This would indicate that the range has been turned on and is set to perform at some operating temperature. Similarly, the contacts 21, 26 may control any other auxiliary circuit, as is common in the art.

A second contact 22. is adapted to be placed in mating engagement with a second fixed contact 28 connected to a tab portion 30 which also passes through the bottom of the housing member 10 to provide a third terminal. Thus the opening and closing of contacts 22 and 28 may control a circuit which includes the terminal connected to ta'b member 23, the main member 20, contacts 22, 28 and the terminal formed by tab member 30. This circuit may form one side of the main line energizing a heater or heating unit, the other side of which is controlled by switch member 18 as will be more fully explained hereinafter. The common support member 20 is formed with a series of bends including a bend 32, 34, 36 wherin the bend 34 forms a cam follower portion. The cam follower portion 34 is adapted to follow the configuration of a camming surface formed on a cam 38 (illustrated in phantom) to provide control of the position of the movable contacts 21, 22 as will be seen from a further description, and particnlarly in conjunction with the description of FIG- URE 6.

As will be seen hereinafter, a depressed portion is formed on the camming surface to provide an off or open position for the contacts 21, 26 and 22, 28 wherein the remainder of the cam surface closes contacts 21, 26 and 22, 28. The bend 36 is provided to realign the contacts 21, 22 with the fixed contacts 26, 28 and in the initial assembly of the switch member this bend 36 is over-emphasized thereby generally urging the contacts 22, 28 and 21, 26 into a closer relation than is normally provided in the final operative switch. Similarly, the contact member 26 is bent at portion 40 wherein the bend 40 is over-emphasized to position the contact 26 closer to the contact 21 than would be normal in the operation of the switch member.

The bends 36, are over-emphasized to provide an initial adjustment of the relative position of the contact 21 with respect to the contact 26 and the contact 22 with respect to the contact 28. Accordingly, when the switch 17 is closed for the first time, the contact member 21 will engage contact 26 as the support member 20 is moved to the right by means of the cam member 38. This initial contact will tend to bend contact member 26 to the right as the support member is flexed. Similarly, the continued motion of the support member 28 brings contacts 22v and 28 into engagement and the further movement of the cam member 38 will thus increase the bend at 36 thereby adjusting the various movable contacts 21, 22 with respect to the fixed contacts 26, 28.

As is seen in FIGURE 2 and in greater detail in FIG- URE 3, switch 18 comprises a composite thermornotive member 42, one end of the thermomotive member 42 being connected to the housing 10 by means of a rivet 64, and the free end carries a relatively movable contact 46. The contact 46 is adapted to cooperate with an adjustably fixed contact 48 attached to one end of a compensator spring or resilient blade 50, the other end of which is suitably riveted to a plate 54, forming a portion of an adjustable calibration means 56.

Composite thermomotive member 42 comprises a bimetallic member 58 and an associated heater strip 60 separated, one from the other, by an insulating member 62. The elements 58, 60 and 62 are secured together at the supported end of member 42 by a rivet 64- which secures member 42 and a terminal member 65 to a support platform 66. Heater strip 60 is connected in series with the switch contacts and with the heating load, and its association with the bimetallic member 58 is such that the successive heating and cooling of the heater strip by the intermittent closing and opening of the contacts under the control of the bimetallic member serves to augment the closing and opening of the switch contacts. This cumulative effect is achieved by imparting an additional force to the contacts due to successive expansion and contraction of the heater strip following closing and opening, respectively.

To assist in this function, a force transmitting member is attached between the free end of heater strip 60 and the free end of bimetallic member 58, as for example, by spot welding. Member 70 is formed to include a spring loop or bite 72. Member 70, bimetallic member 58, contact 46 and a tab 74 are rigidly secured together by any suitable process, as for example, also by spot welding. The assembly of heater strip 60, insulation 62 and bimetallic member 58 is bound together by a winding of fiberglass cord 76. In this manner the transmission of heat from the heater strip 60" to the bimetallic member 58 is greatly enhanced.

The second switch contact is further mounted on a compensator bimetal 80, utilized to compensate for ambient temperatures and forming a cam follower arm. The bimetal includes a free end which is in supporting relation with the contact 48 and a confined end 8-2 which is contained within a portion of the adjusting assembly 56. The arm 80' further includes a cam follower portion 84 which is adapted to be engaged by a camming surface formed on the camming element 38. The camming surface is adapted to successively force contact member 48 into closer and closer engagement with contact 46 thereby requiring a greater amount of heat to separate the contacts 46, 48. In this manner the percentage of power being delivered to the heating element (not shown) is regulated and increases with an increasing force on the cam follower portion 84.

The structure of switch 18 thus far described forms a current operated infinite switch which is adapted to operate cyclically to supply an average power input to the heating element in accordance of the setting of the adjusting cam 58 connected to be controlled by knob 15 and shaft 14. In operation, when cam 38 is rotated from an off position to a position calling for energization of the heating element, the contacts 46, 48 are driven further and further into an overclosure situation.

As is seen particularly from FIGURES 4 and 5, the cam follower portion 84 is adapted to engage a cam race surface 90 which is formed having a portion 92 of greatest depression, which would correspond to a least overclosure position of the switch contacts 46, 48 with the contacts actually being in the open position, to a high heat portion 94 wherein the surface is formed having the least depression thereby providing the greatest force against the cam follower portion 84. In this latter position the switch contacts 46, 48 are provided with the greatest overclosure pressure thereby feeding the heat element or load with the greatest amount of energizing current.

The cam surface 90, between the lowest depression point 92 or off point and the point of greatest heat being supplied to the load 94, is formed as a gradually decreasing amount of depression thereby providing the cam follower portion 84 with a gradually increasing overclosure force. The cam member 38 may be formed of any configuration and is illustrated as being provided with a hollow interior portion to reduce the amount of material utilized in forming the cam member 38, and also is provided with a central aperture. The cam member is adapted to be seated on a shoulder surface 98 formed in a shoulder member 100, and the cam member 38 is resiliently held in position by means of a spring member 182, which is disposed between the cover member 11 and the cam 38. Thus, the cam 38 is resiliently urged toward the shoulder surface 98.

In operation, when the cam member 38 is rotated such that the cam follower portion 84 is moved from the off position at depression 92 to some other position on cam surface 98, the contacts 46 and 48 are urged to the overclosure position wherein the contacts are in engagement and the energization of the heater strip 60 commences. Upon rotation of the cam member 38 the contacts 21, 26 and 22, 28 will also be closed, as will be further explained hereinafter. The orientation of high expansion side of bimetallic member 58 is such that the contacts will open in response to the heating after an interval of time, which time is dependent on the amount of overclosure of the contacts 46, 48. This overclosure is directly related to the position of the cam follower portion 84 with respect to the rotational length of the cam surface 98.

Upon opening of the contacts 46, 48, the bimetal member 58 starts to cool until such time as the contacts 46, 48 are closed and the cycle is again repeated. The ratio of on-time to off-time is determined by the extent of overclosure of the contacts under the influence of cam 38. The circuit through the contacts 46, 48 is completed from terminal 65 to a terminal 186 wherein current flows between terminal 65 and 185 during the period that the contacts 46, 48 are closed and current is interrupted therebetween when the contacts 45, 48 are opened. It is to be understood that any suitable load may be connected to the terminal 65, 106 as for example, the main surface element heater of a range or the like.

Referring now to FIGURES 4 and 6, it is seen that the support arm 20 is similarly actuated as was the support arm 88. Specifically, the cam follower portion 34 of support arm 20 is adapted to ride on a cam surface 118 formed on an interior cam member 112 perpendicular to earn surface 90, the cam surface 112 being formed with a depression 114 which corresponds to the off position, and the remainder of the cam surface is uniformly formed about the radius of the cam member 112. Thus, as the cam follower portion 34 engages depression 114, the contacts 21, 26 and 22, 28 will be in the open position due to the fact that the arm 20 is permitted to move away from the contacts 26, 28. However, when the cam member 38 is rotated, the cam follower portion 34 will be moved out of the depression 114 and onto the remainder on the cam surface 110. Thus, the contacts 21, 26 and 22, 28 will be closed for any position on the cam surface 116* other than theposition wherein the cam follower portion 34 is in engagement with depression 114. It will be noted that the cam 34 is so designed that the engagement of cam follower portion 34 with depression 114 corresponds exactly with the engagement of cam follower portion 84 with depression 92.

Referring now to the specific details of the calibration assembly 56, particularly illustrated in FIGURES 3 and 3A, the calibration assembly 56 generally comprises a calibration clip member 120 which may be formed of any suitable conductive material wherein the clip member 120 includes a bent portion 122, a generally straight leg portion 124 and a generally L-shaped portion 126. The lower end of the L-shaped portion 126 forms the tab 54 to which the compensator spring member 50 is attached. The legs 124 and 126 are bent into such a position that they are generally parallel with respect one to the other, and a space is formed therebetween which is adapted to receive a tab member 130. The tab member 130 is integrally formed with an extension thereon comprising the terminal 106 whereby the tab member 130 passes through the bottom of the housing to provide the projection illustrated at the terminal 106.

Accordingly, the adjustment assembly 122 is adapted to slidingly engage the tab 130 thereby providing an adjustment of the tab 54 with respect to the housing 10. As the tab 54 is moved closer to the bottom of the housing 10, the compensator spring member 50 is also moved closer to the bottom of the housing. The tab 120 is formed with a slot 131 which is adapted to receive a stop member 132, suitably punched from the adjustment member 120 to limit the transverse movement of the member 120 relative to the tab member 139. Each of the legs 124 and 126 is provided with apertures 136, 138 to receive the lower portion 82 of the compensator bimetal member 8'!) thereby establishing a relatively adjustable pivot for the compensator bimetal element 80.

As was stated above, the cam follower portion 84 of the compensator bimetal is adapted to engage the cam member 38 thereby providing a pressure point for the compensator bimetal 80. Accordingly, for a fixed pressure or a position of the cam follower portion 84 and thus the contact 48, the adjustment assembly 56 may be moved upwardly or downwardly to then adjust the relative position of the contact 48. Thus as the member is moved downwardly, pressure is relieved from the contact 48 to cause the contacts to open. Similarly, if the member 120 is raised to its uppermost position, as shown, the contacts 46 and 48 will be in their greatest overclosure position and require the greatest amount of heat to separate the contacts 46, 48. In initially assembling the switch unit, the adjustment assembly 56, including the element 120, is forced to its uppermost position. The cover is then placed on the switch and the switch is ready for final adjustment.

In making the final adjustment, the switch 10 may be placed into an automatic calibrating apparatus such as that illustrated in application Ser. No. 495,027, filed Oct. 7, 1965. As was stated above, the calibration clip 120 is initially set at its maximum overclosure position wherein the tab 54 is furthest from the rivet 64. The operator then sets the knob 15, and accordingly the cam assembly 38, at a preselected heating affect condition, as for example a position which is preselected to give a simmer condition on the surface heater element. Then a measured pulse of power, as for example, 15 watt-seconds, is applied through the switching apparatus to simulate the normal operating conditions of the switch. For example, a switch may be normally operated at 0.4 of a Watt continuously and this condition is simulated in the calibration area by the application of approximately 10 watts for 1 /2 seconds.

With the contacts 46, 48 in the overclosure position, a sensing indicator is applied to the terminals 65, 1136 which is controlled by the opening and closing of the contacts 46, 48. Thus, an accurate indication of the closed or opened condition of the contacts may be obtained. With the above heat being applied to the bimetal through the switch contacts 46, 48, an automatic pusher assembly, such as that described in the aforementioned patent application, is utilized to apply a force to the calibrator clip 120 through aperture 13 in an opening direction Thus with a constant heat pulse being applied to the bimetal 58, thereby tending to open contacts 46, 48, the calibrator clip 120 is moved downwardly until such time as the contacts 46, 48 are just opened. This opening of the contacts is indicated by the sensing indicator connected to the terminals 55, 106.

The configuration of calibrator climp 129 is of such a nature that approximately pounds pressure is required to move the clip 120 on the tab member 130. Thus, it is held firmly against any of the smaller forces encountered in the use of switches which would tend to displace the calibrator clip 120. As is readily apparent in the case of an infinite switch such as the one described, the heating of the pulse may be accomplished conveniently by the energization of the resistor heater associated therewith. The switches which do not include a resistance heater, separate heating means or other types of heating means may be provided.

It is also obvious that similar means may be utilized to calibrate a thermally activated switch whose thermomotive member is adapted to close the contacts when heated. In such a case, the calibrator clip 12?. is initially located at a point wherein the contacts are in an open position and the force from the switching assembly is applied in such a manner as to move the contacts toward a closed position. Suitable provision may be made for automatically opening the drive circuit of the switching apparatus when such closure is accomplished.

It is to be noted that the above described switch provides a compact, electrically insulating switch structure which is reliable in operation and inexpensive to construct. The terminal members 23, 65, 166 are so positioned as to permit several switches to be electrically connected together in a multiple configuration by a buss bar interconnecting common terminals of each switch. Also, the resilient member 162 is so positioned as to minimize the number of elements required to provide the resilient force necessary to position cam member 38,

While it will be apparent that the embodiments of the invention herein disclosed are well calculated to fulfill the objects of the invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subjoined claims.

What is claimed is:

1. A condition responsive switch comprising a pair of relatively movable contacts, first support means for supportin one of said contacts, second support means for supporting the other of said contacts, said first support means including deflectable blade means and condition responsive means for causing deflection of said blade means and control of the position of the respective one of said contacts in response to a condition, and calibration means coupled to one of said first and second support means for initially calibrating the relative positions of said contacts including support tab means fixedly supported relative to the other of said first and second support means and calibrating clip means slidably supported on said support tab means, and means controlled by the movement of said clip means and fixed to the one or" said first and second support means for moving said one support means relative to said other support means in response to sliding movement of said clip means on said support tab means.

2. The switch of claim 1 wherein said one of said first and second support means is said second support means.

3. The switch of claim 1 wherein said calibrating clip means includes first and second leg portions spaced, one from the other, for forming a friction channel.

4. The switch of claim 3 wherein said first and second leg portions are in frictional engagement with opposite portions of said support tab means for frictionally fixing said other of said first and second support means in a selected calibration position relative to said one of said first and second support means.

5. The switch of claim 4 wherein said calibrating clip means includes a mounting portion for rigidly mounting a portion of said one of said first and second support means at a point spaced from the respective supported contact.

6. The switch of claim 5 wherein said second support means includes a first support arm and a second support arm, said second support arm being rigidly mounted on said calibrating clip means for sliding movement relative to said support tao means and establishing a calibrated relation between said first and second support means and said first support arm having follower means thereon adapted to be responsive to an external force for variably changing the relationship of said contacts and varying the operation of said switch.

7. The switch of claim 6 wherein said calibrating clip means includes spacing means for limiting the degree of movement of said first support arm toward said second support arm.

8. The switch of claim 7 wherein said first support arm is a compensating bimetal and said second support arm is a spring member for urging said first support arm toward said second support arm.

9. The switch of claim 8 wherein said calibrating clip means includes means forming an aperture in said first and second leg portions for receiving an end of said first support arm at a point spaced from said respective contact and said support tab means having means forming an aperture therein for receiving said end of said first support arm.

References Cited UNITED STATES PATENTS 1/1939 Payne 200l39 12/1957 Turner 200l22 

1. A CONDITION RESPONSIVE SWITCH COMPRISING A PAIR OF RELATIVELY MOVABLE CONTACTS, FIRST SUPPORT MEANS FOR SUPPORTING ONE OF SAID CONTACTS, SECOND SUPPORT MEANS FOR SUPPORTING THE OTHER OF SAID CONTACTS, SAID FIRST SUPPORT MEANS INCLUDING DEFLECTABLE BLADE MEANS AND CONDITION RESPONSIVE MEANS FOR CAUSING DEFLECTION OF SAID BLADE MEANS AND CONTROL OF THE POSITION OF THE RESPECTIVE ONE OF SAID CONTACTS IN RESPONSE TO A CONDITION, AND CALIBRATION MEANS COUPLED TO ONE OF SAID FIRST AND SECOND SUPPORT MEANS FOR INITIALLY CALIBRATING THE RELATIVE POSITIONS OF SAID CONTACTS INCLUDING SUPPORT TAB MEANS FIXEDLY SUPPORTED RELATIVE TO THE OTHER OF SAID FIRST AND SECOND SUPPORT MEANS AND CALIBRATING CLIP MEANS SLIDABLY SUPPORTED ON SAID SUPPORT TAB MEANS, AND MEANS CONTROLLED BY THE 